With scorching summers and damp winters, the need to cool, heat and combat humidity makes air conditioning virtually a necessity in many Algarve properties. Even for buildings with excellent thermal insulation qualities, requiring lower-capacity systems, there's still a need to cool or heat the ambient air. With this in mind it makes sense to consider the most efficient machines possible.

In fact, today's air conditioning systems are among the most energy-efficient ways to cool and heat your home. In recent years, 'inverter' systems have become commonly available from all brands, offering energy (i.e. electricity) savings of up to 40% compared to non-inverter models.

With non-inverter machines, the outside compressor unit operates at a fixed speed, simply switching on and off repeatedly in order to keep around the temperature required. This 'start-stop' way of operation is expensive in terms of running costs.

Instead, today's inverter systems have a variable-speed compressor coupled with 'smart' technology which monitors the room temperature. This regulates the compressor's speed, which is constantly operating but accelerating or slowing down as necessary to maintain a selected temperature. Inverter systems therefore hold to a more precise room temperature, without the fluctuations of a fixed-speed system (see diagram).

Because of this more sophisticated technology, inverter systems are more expensive to buy. But, if in frequent use, the energy savings they bring are significant and worthwhile. Look for the word 'inverter' and for a category-A energy rating label on its packaging.

Inverter systems are often advisable for holiday rental properties, as clients tend to run air conditioning much of the time and at full capacity, with no responsibility for energy bills.

Inverters bring another benefit too: lower noise levels. Quieter than ever, today's internal units operate at around 20 decibels – around the level of a human whisper. This is often an important factor in bedrooms, where whirring systems can cause disturbed or sleepless nights. Again, inverters are a sensible precaution in bedrooms of holiday rental properties.

Air conditioners not only provide cooling but, just as importantly in the Algarve's chilly winters, they provide effective heating too. Another myth is that air conditioners are an expensive way to heat – not so! In fact, using an inverter-type system is actually more cost-effective than underfloor heating. Inverter units have a COP-rating ('Coefficient Of Performance') of as much as 5, meaning that, in effect, for every euro's worth of energy you put in you get 5 euros' worth of energy out. This is much the same as an electric heat exchange water heater – not surprising, as they use similar technology.

De-humidifying is a natural consequence of air-con heating too – another advantage in the Algarve's humid climate. De-luxe models nowadays incorporate additional systems, operating independently of the air con, which cleanse the air of dust, impurities and even odours. Furthermore some systems can be operated remotely, allowing absent owners to maintain an optimal 'indoor climate' for their property.

As with any type of heating or cooling system, regular maintenance is always necessary. A standard service is inexpensive and always recommended to ensure that the air con in your home is running at full energy-efficiency.